Conventional flush valves used with water closets, urinals and the like suffer from a number of shortcomings. For example, such flush valves require a second unit including a vacuum breaker valve or anti-siphon valve to be installed between the flush valve and water closet. This requires the manufacture of a separate unit, at additional cost to the user and, perhaps even more importantly, requires a second additional installation by a plumber which, in view of present charges for plumbing services, is a substantial expense. Such flush valves also require another, third unit to prevent unpredictable surges or increases in line pressure from causing unwanted actuation of the flush valve. This unwanted actuation is particularly troublesome when it occurs as a result of a sudden increase in line pressure or when normal line pressure is restored after the line has been drained. Under these conditions, the control chamber drains and loses pressure so that a subsequent surge or increase in pressure is able to overcome pressure in the control chamber and cause unwanted actuation of the flush valve. Again, the increased cost of this third separate unit, and the increased charge for installation, adds significantly to the user's cost. Often this third unit contains some sort of flow control device for setting the volume of water discharged per flush at the particular pressure of the supply line. This setting is done at installation by a plumber.
Presently available flush valves are difficult to actuate because the actuator is opposing line pressure. The force required for this may be difficult to apply for the young, the aged, and the infirm. In addition, the actuator mechanism functions to open, but not to close, the flush valve actuator valve. Another disadvantage of contemporary flush valves is that they must be made and stocked in each of a number of configurations with respect to the relative arrangement of the actuator handle and supply line.